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authorShachar Raindel <shacharr@microsoft.com>2021-03-13 02:45:27 +0300
committerDavid S. Miller <davem@davemloft.net>2021-03-15 00:32:37 +0300
commitbd49fea7586b9d39a38846e9ef4ac056e4eb6e59 (patch)
tree2f24bccd2826e7b7080342dbeaf9e40c73a29c3c /drivers
parent0f88e6f35b314500ba4c2f7d62c4598bf2c1229b (diff)
downloadlinux-bd49fea7586b9d39a38846e9ef4ac056e4eb6e59.tar.xz
hv_netvsc: Add a comment clarifying batching logic
The batching logic in netvsc_send is non-trivial, due to a combination of the Linux API and the underlying hypervisor interface. Add a comment explaining why the code is written this way. Signed-off-by: Shachar Raindel <shacharr@microsoft.com> Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com> Reviewed-by: Dexuan Cui <decui@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/net/hyperv/netvsc.c20
1 files changed, 20 insertions, 0 deletions
diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index c64cc7639c39..5bce24731502 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -1017,6 +1017,26 @@ static inline void move_pkt_msd(struct hv_netvsc_packet **msd_send,
}
/* RCU already held by caller */
+/* Batching/bouncing logic is designed to attempt to optimize
+ * performance.
+ *
+ * For small, non-LSO packets we copy the packet to a send buffer
+ * which is pre-registered with the Hyper-V side. This enables the
+ * hypervisor to avoid remapping the aperture to access the packet
+ * descriptor and data.
+ *
+ * If we already started using a buffer and the netdev is transmitting
+ * a burst of packets, keep on copying into the buffer until it is
+ * full or we are done collecting a burst. If there is an existing
+ * buffer with space for the RNDIS descriptor but not the packet, copy
+ * the RNDIS descriptor to the buffer, keeping the packet in place.
+ *
+ * If we do batching and send more than one packet using a single
+ * NetVSC message, free the SKBs of the packets copied, except for the
+ * last packet. This is done to streamline the handling of the case
+ * where the last packet only had the RNDIS descriptor copied to the
+ * send buffer, with the data pointers included in the NetVSC message.
+ */
int netvsc_send(struct net_device *ndev,
struct hv_netvsc_packet *packet,
struct rndis_message *rndis_msg,